One hen lays fishy smelling eggs

[Petra Pancake]

In recent weeks, I've noticed that one of my Japanese Bantam hens lays fishy smelling eggs . They are practically inedible. She lives in an aviary together with the second Bantam hen. The second one lays eggs that maybe have a very faint fish smell but are still edible. I can't compare to my other hens who live in a separate run because those are not laying now for various reasons.
The two Bantams get layer feed and bits of grass clippings and vegetables. No fish, of course.
Their layer feed does not contain canola meal or rapeseed meal according to the label.
Any ideas what causes the fishiness?
Why just one hen and not the other? They are mother and daughter.

 

[heidibee]

I copied this response from a thread on reddit (https://www.reddit.com/r/AskCulinary/comments/4oeo2u/fishy_tasting_eggs/):

"Fishy" taste is due to the presence of trimethylamine (TMA).

The reason some hens lay eggs with high amounts of TMA boils down to diet and genetics.

Poultry require an essential vitamin called choline to live. Choline is regularly added to the feed of poultry as a supplement.

Some hens deposit large amounts of TMA in their eggs when fed large amounts of choline. This is due to genetics.http://www.ncbi.nlm.nih.gov/pubmed/23436525

So, long story short, you sometimes get fishy eggs because the hens are fed a lot of choline, and because for some of those chickens, their DNA predisposes them to metabolizing choline into TMA (among other things) and depositing it into their eggs.

 

[aart]

I believe that cottonseed meal in feed can make for 'fishy eggs'.